The pathogenesis, molecular biology, immunology, natural history, and therapy of human herpesvirus infections are being investigated. Immunocompetent and immunodeficient patients with a wide range of herpesvirus infections have been identified, followed clinically, diagnosed by virus isolation, and studied immunologically. During the past year we have made major advances in the treatment of selected patients with herpes simplex infections using a new drug, acyclovir. Our major focus on the study of the molecular biology and latency of varicella zoster virus DNA has continued. During the past year we have completed restriction endonuclease analyses and molecular epidemiologic studies of 19 strains of varicella zoster virus DNA. We have molecularly cloned a library of varicella zoster DNA fragments and have completed the mapping of the varicella zoster virus genome. We are now using these recombinant clones for rapid diagnosis of varicella and zoster infections and as probes of human tissues to determine the sites and nature of viral latency.